It was the opposite experience for me. Before spellcheck was commonly part of the web browser, I would go back and reread some very early emails and/or usenet posts from myself. And realize how atrocious my spelling was.

I actually consider spellcheck to have improved my spelling dramatically over the years. The little red squiggles under words have helped me to recognize my misspellings, especially the words that are hard for me to get right consistently.